The present invention relates to an optical motion detector, transport system, and transport processing system, for detecting a paper feed speed and the quantity of movement of paper in a variety of equipment such as a printer and a copier or measuring in a non-contact manner the speed and the quantity of movement of another object whose surface is not a mirror surface.
Conventionally, as shown in FIG. 9, there has been an optical motion detector that has two distance measuring sensors 101 and 102 and a processing unit 103. The principle of the distance measuring sensors 101 and 102 of this optical motion detector will be described with reference to FIG. 10. As shown in FIG. 10, the distance measuring sensors 101 and 102 have a light-emitting section 104, a lens 105 that concentrates diffused light from the light-emitting section 104, a light-receiving section 107 that receives light reflected on a measurement object 106 and a lens 108 that concentrates the reflected light from the measurement object 106 on the light-receiving section 107. In this case, a light beam from the light-emitting section 104 is perpendicularly incident on the measurement object 106, and the reflected light from this position is concentrated on the light-receiving section 107 by the lens 108. The light-receiving section 107 employs a PSD (Position Sensitive Device; position detection device), and a ratio of a first output and a second output varies in correspondence with the position of the spot light concentrated on the light-receiving surface. A distance can be measured by utilizing the phenomenon that the ratio of first output/second output varies in accordance with the distance between this PSD and the measurement object.
In FIG. 9, if the measurement object 106 moves in the direction of arrow, then the two distance measuring sensors 101 and 102 obtain outputs corresponding to the unevenness of the measurement object 6, and these outputs representing the distance between the distance measuring sensors 101 and 102 and the measurement object 106, fluctuate corresponding to the quantity of unevenness. As shown in FIGS. 11A and 11B, with regard to the output waveforms obtained at this time, the distance measuring sensor 102 of B (shown in FIG. 11B) has an output waveform delayed by xcex94t from that of the distance measuring sensor 101 of A (shown in FIG. 11A) in accordance with the travel speed of the measurement object 6. This delay xcex94t is calculated by the processing unit 103 to obtain the travel speed and the quantity of movement of the measurement object 106.
The aforementioned optical motion detector, which needs the two distance measuring sensors 101 and 102 that employ the light-emitting section 104, the light-receiving section 107 and the two lenses 105 and 108, has a problem that it has many components and a large size in terms of shape, which leads to high manufacturing cost. Moreover, there is a problem that a measurement object having a comparatively smooth surface (surface having minute unevenness) is hard to measure, dissimilarly to the fortunate case where the measurement object has an uneven surface that can be detected as a difference in distance by the distance measuring sensors 101 and 102.
Furthermore, although there is a laser Doppler type as another conventional optical motion detector, this laser Doppler type optical motion detector is large in size and expensive.
Accordingly, the object of the present invention is to provide an optical motion detector, transport system and transport processing system capable of reducing the number of components with a simple construction, reducing the size and cost and measuring at least one of the travel speed and the quantity of movement of a measurement object even when the measurement object has a comparatively smooth surface unless the measurement object has a surface of mirror state.
In order to achieve the above object, there is provided an optical motion detector comprising:
a light-emitting device;
a collimator lens for collimating a light beam emitted from the light-emitting device;
an object lens, which concentrates the light beam collimated by the collimator lens and applies the light beam to a measurement object that moves in a prescribed direction, forming a light spot that has a prescribed spot diameter on the measurement object;
a beam splitter, which splits a reflected light which belongs to a reflected light from the light spot of the measurement object and is concentrated via the object lens;
a light-receiving lens, which concentrates the reflected light split by the beam splitter;
two pinholes, through which reflected lights pass, wherein the lights belong to the reflected light concentrated by the light-receiving lens and come from two regions inside the light spot located at a prescribed interval on a straight line parallel to a measurement object travel direction;
two light-receiving sections on which the reflected lights, which have passed through the two pinholes, are respectively made incident; and
a measuring section, which measures at least one of a travel speed and a quantity of movement of the measurement object on the basis of outputs of the two light-receiving sections.
According to the optical motion detector of the above-mentioned construction, the light beam emitted from the light-emitting device is collimated by the collimator lens and thereafter applied to a measurement object that moves in the prescribed direction via the object lens, forming a light spot on the measurement object. Among the reflected light from this light spot, the reflected light concentrated via the object lens is split by the beam splitter and concentrated by the light-receiving lens. Thereafter, only the reflected light from the two regions located at the prescribed interval on the straight line parallel to the measurement object travel direction inside the light spot is made to pass separately through the two pinholes, and the reflected light that has passed through the two pinholes is made incident on two light-receiving sections. Then, on the basis of the outputs of the two light-receiving sections, at least one of the travel speed and the quantity of movement of the measurement object is measured by the measuring section. That is, when the measurement object moves, one output waveform of the output waveforms detected by the two light-receiving sections has a shape delayed timewise from the other output waveform. By preparatorily setting a distance between the two regions inside the light spot, the travel speed or the quantity of movement of the measurement object can be obtained on the basis of the time of delay of the output waveform of this light-receiving section and the distance between the two regions inside the light spot. Therefore, the number of components of the motion detector can be reduced with a simple construction, and this allows a size reduction in terms of shape and a reduction in manufacturing cost to be achieved. Moreover, even a measurement object that has a comparatively smooth surface can be measured unless the surface state (state of unevenness) of the measurement object is a mirror surface.
In one embodiment of the present invention, the light-emitting device is a semiconductor laser device.
According to the optical motion detector of the above-mentioned embodiment, which employs the light-emitting device of a semiconductor laser that has a small light-emitting section and is tantamount to a point light source, is therefore able to efficiently concentrate light by the lens and obtain a quantity of reflected light required for the signal detection by the light-receiving device from the measurement object.
In one embodiment of the present invention, an optical axis of emitted light concentrated by the object lens is perpendicular to the measurement object.
According to the optical motion detector of the above-mentioned embodiment, the optical axis of the emitted light, which is concentrated by the object lens and applied to the measurement object moving in the prescribed direction, is approximately perpendicular to the measurement object. Therefore, the depth of focus becomes deep, and even if the interval between the measurement object and the object lens is varied due to the positional variation of the measurement object, the variation in the shape of the light spot on the measurement object can be reduced further than when the light beam is not applied perpendicularly to the measurement object.
In one embodiment of the present invention, the measurement object is located in a position farther apart from the object lens than a focal position of the emitted light concentrated by the object lens.
According to the optical motion detector of the above-mentioned embodiment, the measurement object is located in a position farther apart from the object lens than the focal position in which the light beam is concentrated by the object lens. Therefore, the optical system, which is able to secure the two regions located at the prescribed interval on the measurement object and concentrate the reflected light from these two regions by the object lens, can be formed.
In one embodiment of the present invention, the two light-receiving sections are provided in one light-receiving device, and
the two pinholes are formed in a mask provided on light-receiving surfaces of the two light-receiving sections.
According to the optical motion detector of the above-mentioned embodiment, the mask is provided on the light-receiving surfaces of the two light-receiving sections provided for the one light-receiving device, and the two pinholes are formed in the positions of the mask corresponding to the two light-receiving sections of the light-receiving device. Since the two pinholes and the light-receiving device (having the two light-receiving sections) are integrated with each other, pinholes of high accuracies of size and position can be achieved, and this allows the achievement of cost reduction than when the pinholes are provided in separate members.
In one embodiment of the present invention, a size A of the two regions located at the prescribed interval on the straight line parallel to the measurement object travel direction inside the light spot has a diameter of not smaller than 10 xcexcm and not greater than 100 xcexcm, and
a size of the two pinholes is a size obtained by the size A of the two regions and an optical image formation formula.
According to the optical motion detector of the above-mentioned embodiment, the size A of the two regions inside the light spot is not smaller than 10 xcexcm and not greater than 100 xcexcm, and the size of the two pinholes is obtained by the above-mentioned size A and the optical image formation formula. Therefore, a signal of sufficient absolute quantity and signal-to-noise ratio can be obtained, and the change in the surface state of the measurement object can reliably be detected. In this case, assuming that a distance from an object to the lens is L1 and a distance from the lens to the image is L2 when the object forms an image on the opposite side via the lens, then the optical image formation formula expresses the relation that the magnification (ratio of the image size to the object size) is L2/L1.
In one embodiment of the present invention, an interval B between centers of the two regions located at the prescribed interval on the straight line parallel to the measurement object travel direction inside the light spot satisfies the condition of:
Axe2x89xa6Bxe2x89xa6Sxc2x7A/tan xcex8
(where S is a ratio of a quantity of relative displacement of the two regions inside the light spot in a perpendicular direction to the measurement object travel direction within a plane thereof with respect to A, xcex8 is an angle made between the measurement object travel direction and a prescribed travel direction, and 0.4 greater than S greater than tan xcex8).
According to the optical motion detector of the above-mentioned embodiment, assuming that the ratio of the quantity of relative displacement of the two regions inside the light spot in the perpendicular direction to the measurement object travel direction within the plane thereof with respect to A is S, an angle made between the measurement object travel direction and a prescribed travel direction is xcex8 and 0.4 greater than S greater than tan xcex8 when the region of the size A is displaced on the measurement object, then an interval B between the centers of the two regions ranges from A to Sxc2x7A/tan xcex8. Accordingly, there can be achieved the detection of the measurement object with a small error against displacement of the actual travel direction with respect to the prescribed travel direction.
In one embodiment of the present invention, the two pinholes have an oval shape or a rectangular shape whose longitudinal direction is approximately perpendicular to the measurement object travel direction.
According to the optical motion detector of the above-mentioned embodiment, the displacement of the actual measurement object travel direction with respect to the prescribed travel direction becomes a displacement in a direction approximately perpendicular to the prescribed travel direction of the measurement object. By making the two pinholes have the oval shape or the rectangular shape of which the longitudinal direction is approximately perpendicular to the measurement object travel direction instead of a round shape, the error of the information of the surface state of the measurement object is reduced, and the detection can be achieved with a small error with respect to the displacement.
In one embodiment of the present invention, the optical motion detector is provided with a casing for guiding the measurement object.
According to the optical motion detector of the above-mentioned embodiment, the casing that guides the measurement object so that the measurement object is located in the position the prescribed distance apart from the object lens. Therefore, the variation in the distance between the measurement object and the object lens can be reduced, and this allows the reduction in the variations of the size A of the two regions and the interval B between the centers thereof inside the light spot and allows accurate detection to be achieved.
In one embodiment of the present invention, when the measurement object is transported by a transport unit, the speed of the measurement object is controlled by the transport unit on the basis of a signal that represents at least one of the travel speed and the quantity of movement of the measurement object measured by the optical motion detector.
According to the transport system of the above-mentioned construction, by feeding back at least one of the travel speed and the quantity of movement of the measurement object measured by the aforementioned optical motion detector to the transport system, there can be provided the transport system that accurately controls at least one of the travel speed and the quantity of movement of the measurement object.
In one embodiment of the present invention, when the measurement object is subjected to processing by a processing unit while the measurement object is transported, the processing of the measurement object is performed in a prescribed position by the processing unit on the basis of a signal that represents at least one of the travel speed and the quantity of movement of the measurement object measured by the optical motion detector.
According to the transport processing system of the above-mentioned construction, when the measurement object is subjected to some processing while the measurement object is transported, at least one of the travel speed and the quantity of movement of the measurement object measured by the optical motion detector is fed back to the processing unit to control the timing of the processing. Therefore, a transport processing system, which can accurately perform the processing of the measurement object in the prescribed position, can be achieved.